Pressure graduated control valve

ABSTRACT

An axial slot with enlarged end openings is formed in a valve spool of a control valve having inlet, service and exhaust ports spaced axially along the valve spool bore. The axial slot always communicates with the service port and extends axially a sufficient distance to permit communication between all three ports as the valve spool is moved from its closed position to its open position. In the closed position one end of the slot is blocked and the other opens into the exhaust port. In the open position said one end of the slot is open to the inlet port and the other end of the slot is blocked from communication with the exhaust port. The valve provides rapid pressure rises in the service port during initial and final movements of the spool from its closed position to its open position.

United States Patent 1191 Carl [ PRESSURE GRADUATED CONTROL VALVE [75] Inventor: David F. Carl, Springfield, 111.

[73] Assignee: Allis-Chalmers Corporation,

Milwaukee, Wis.

[22] Filed: Feb. 1, 1.973

[21] Appl. No: 328,760

[52] US. Cl..... l37/625.68, 137/6253, l37/625.69, 251/325 [51] Int. Cl. Fl6k 11/07 v [58] Field of Search ..137/625.28-625.39.

[ Oct. 16, 1973 4/1965 Spokas 137/625.69 2/1968 Flint ..137/625.25

Primary Examiner-Henry T. Klinksiek Attorney-Charles L. Schwab et a1.

a valve spool of a control valve having inlet, service and exhaust ports spaced axially along the valve spool bore. The axial slot always communicates with the service port and extends axially a sufficient distance to permit communication between all three ports as the valve spool is moved from its closed position to its open position. In the closed position one end of the slot is blocked and the other opens-into the exhaust port. In the open position said one end of the slot is open to the inlet port and the other end of the slot is blocked from communication with the exhaust port. The valve provides rapid pressure rises in the service port during initial and final movements of the spool from its closed position to its open position.

12 Claims, 5 Drawing Figures PATENTEDUET 18 I973 SHEET 1 [If 2 PATENTEDUBT 6 I973 SHEET 2 BF 2 RELIEF VALVE PRESSURE;

SPOOL D\SPLACEMENT 1 PRESSURE GRADUATED CONTROL VALVE BACKGROUND OF THE INVENTION Heretofore others have used various recesses and slots in the spools of control valves to obtain a modulated or graduated pressure rise in the working fluid.

Included in the prior art is the variable flow modulated valve shown in US. Pat. No. 3,556,]55.

BRIEF DESCRIPTION OF THE INVENTION An axial slot is formed in the spool of a control valve so as to extend, in the closed position ofthe spool, from a position adjacent an inlet port across a service port and into an exhaust port. The opposite axial ends of the slot are enlarged in width by drilling holes in the spool of a diameter greater than the width of the slot. The drilled opening at the inlet end of the slot is blocked by a land of a bore in which the valve spool reciprocates when the latter is in its closed position. As the valve is moved toward an open position initial movement provides a rapid pressure rise for initial movement of the valve. As the valve spool is moved further toward its open position the pressure rise is more gradual in relation to spool movement and then as the drilled opening at the exhaust end of the slot is moved into a confronting or blocked relationship with a land in the bore a.

high rate of pressure rise is achieved. Such a pressure versus spool displacement relationship is desirable in hydraulic controls for steering clutches of crawler tractors.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is shown in the two sheets of drawings in a pair of control valves. More specifically:

FIG. 1 is a section view showing a pair of steering control valves for a crawler tractor in their closed position;

FIG. 2 shows one of the steering control valve spools shifted slightly toward an open position;

FIG. 3 is a section taken along the line III-III in FIG. 2;

FIG. 4 is a view similar to that of FIG. 2 but showing the spool moved to a full open position; and

FIG. 5 is a pressure versus spool displacement graph.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. I, a pair of steering clutches 11, 12 in the final drive housing 13 of a crawler tractor are controlled by a hydraulic control system including a valve assembly 16. The valve assembly 16 includes a valve body 17 having a pair of bores 18, 19 in which a pair of valve spools 2.1, 22 are mounted for axial reciprocation between open and closed positions. A pump 23 draws fluid from final drive housing 13, which serves as a reservoir, by way ofline 24 and delivers fluid under pressure via line-25 to an inlet passage 27 which is connected to inlet ports 28, 29 formed in the body 17. A pair of service ports 31, 32 are formed in the body in intersecting relation to the bores l8, l9 and are in axially spaced relation to the inlet ports 28, 29. The ser vice ports 31, 32 are connected to the clutches 11, 12 through appropriate conduits shown schematically by lines 33, 34. A pair of exhaust ports 36, 37, spaced axially of the service ports 31, 32, are connected to one another by an internal passage 38 and are connected by an internal passage 39 to an outlet 41 in the body 17 which in turn is connected to the final drive housing 13 by an exhaust conduit 42. Conventional biasing means 51, 52 are provided on the right ends of the valves 21, 22 to bias the valve spools 21, 22 to their illustrated closed positions. The valve assembly 16 also includes an unloading valve 56 and a high pressure relief valve 57.

When both of the valve spools 21, 22 are in their closed position, as illustrated in FIG. 1, the pressure in chamber 61 will be that of the exhaust outlet 39 and thus only the spring 62 urges the unloading valve 56 toward its illustrated closed position. Thus a relatively low pressure in inlet passage 27 will open the unloading valve 56 to dump fluid from the pump inlet 27 to an exhaust passage 63 which is connected to passage 38 by the exhaust port 37.

Referring also to FIGS. 2, 3 and 4, a pair of diametrically opposite and axially extending slots 71, 72 are formed in the spool 21, as by milling, so as to be of sufficient axial dimension to bridge the distance between inlet port 28 and exhaust port 36 during movement of the spool 21 from its closed position to its open position. A pair of drilled openings 73, 74 extend radially in relation to the spool 21 and interesect its axis 75. The diameters of the openings 73, 74 are greater than the width x of the slots 71, 72. The slots 71, 72 have indentical widths. In the closed position of the spool 21, the opening 73 at the inlet end of the slots is blocked by a land 76 of the bore 18, whereas opening 74 at the outlet end of the slots is in full free flow communication with the exhaust port 36. If the spool 21 is moved to a slightly open position such as shown in FIG. 2, wherein about one-half of opening 73 is exposed to the inlet port 28, the pressure in the service port 31 will rise rapidly in relation to spool displacement. The point A on the pressure versus spool displacement curve, shown in FIG. 5, corresponds to the position of the valve in FIGS. 2 and 3. The rapid initial rise in pressure in the service port 31 is highly desirable in crawler tractor steering clutch operation. As the spool is moved from the position shown in FIG. 2 to near the position shown in FIG. 4, the pressure in service port 31 will rise more gradually as illustrated by the central part of the curve shown in FIG. 5. 'As the opening 74 becomes blocked by a land 77 of the bore 18, the pressure will rise rapidly in the service port 31. This rapid pressure rise in the final spool movement is also highly desirable in steering clutch control. The upper limit of the pressure in the service port 31 is established by the relief valve 57 and such pressure is indicated in FIG. 5 by a dash line labeled relief valve pressure.

In the preferred embodiment of the present invention, an annular recess 81 is provided in the spool 21 in spaced relation to the inlet and outlet openings 73, 74. The annular recess 81 is in direct communication with service port 31 in all positions of the spool 21, but does not open into either the inlet port 28 or the exhaust port 36 in any operating position of the spool 21. The recess 81 communicates with the openings 73, 74 only through the slots 71, 72.

In summary, the present invention provides a valve spool having an axial slot which is always in fluid communication with the service port. The slot also communicates with the exhaust port in the closed position of the valve spool and with the inlet port in the spools open position. The slots inlet and outlet ends, that is the axially opposite ends, are enlarged to provide a more rapid pressure rise, in relation to valve spool movement, during initial and final movements of the spool from closed to open positions. The inlet, service and exhaust ports arespaced axially of one another along the spool bore and communicate with the bore. The inlet and service ports 28, 31 are separated by the bore land 76 and the service and exhaust ports 31 and 36 are separated by the bore land 77. The bore land 76 cooperates with spool land 82 to prevent fluid flow from the inlet port 28 to the service port 31 in the closed position of the spool 31 as illustrated in FIG. 1. The bore land 77 cooperates with spool land 83 to prevent flow from the service port 31 to exhaust port 36 when the spool 21 is in its closed position as shown in FIG. 4. The slots 71, 72 and enlarged peripheral openings 73, 74 at their axially opposite ends provide a generally gradual pressure rise in the service port 31 as the spool 21 is moved from its closed to open position with the pressure rise being relatively rapid in the initial and final movement of the spool from closed to open positions. This invention provides an excellent pressure versus displacement relationship for crawler tractor hydraulic steering clutch control.

The embodiments of an invention in which an exclusive property or privilege is claimed are defined as follows:

l. A control valve of the type having a body with a bore, an inlet port communicating with said bore, a service port communicating with said bore and spaced in one axial direction from said inlet port by a first bore land and an exhaust port communicating with said bore and spaced in said one axial direction from said service port by a second bore land, characterized by:

a spool reciprocatively mounted in said bore for axial movement between closed and open positions and having an axially extending slot in its periphery in communication with said service port, and

first and second enlarged peripheral openings in said slot at its opposite axial ends, respectively, said first opening being blocked by said first bore land and said second opening being in full free flow communication with said exhaust port when said spool is in its closed position, said first opening being in full free flow communication with said inlet port and said second opening being blocked by said second bore land when said spool is in its open position.

2. The valve of claim 1 and further characterized by an annular recess in said spool between and spaced axially from said openings.

3. The valve of claim 2 wherein said recess communicates directly only with said service port and said recess is in fluid communication with said openings only through said slot.

4. The valve of claim 1 wherein said openings are annular and extend transversely relative to the axis of said spool, the diameter of said openings being greater than the width of said slot.

5. The valve of claim 4 wherein said openings extend transversely through said spool.

6. The valve of claim 5 and further characterized by another slot on the diametrically opposite side of said spool'from said first mentioned slot and extending axially between and in free flow communication with said openings.

' one axial direction from said inlet port by a first bore land and an exhaust port communicating with said bore and spaced in said one axial direction from said service port by a second bore land, characterized by;

a spool reciprocatively mounted in said bore for axial movement between closed and open positions and having, an axially extending slot in its periphery in communication with said service port, said slot being blocked from communication with said inlet port by said first bore land and said slot being in full free flow communication with said exhaust port when said spool is in its closed position, said slot being in full free flow communication with said inlet port and said slot being blocked from communication with said exhaust port by said second bore land when said spool is in its open position, said slot being in fluid communication with all said ports during a major part of the movement of said spool from said closed position to said open position.

8. The valve of claim 7 and further characterized by an annular recess in said spool intermediate the axially other-slot is enlarged at its axial end nearest said exopposite ends of said slot.

9. The valve of claim 8 wherein said recess communicates directly only with said service port and said recess is in fluid communication with said inlet and exhaust ports only through said slot.

10. A control valve of the type having a body with a bore, an inlet port communicating with said bore, a service port communicating with said bore and spaced in one axial direction fromsaid inlet port by a first bore land and an exhaust port communicating with said bore and spaced in said one axial direction from said service port by a second bore land, characterized by:

a spool reciprocatively mounted in said bore for axial movement between closed and open positions and having a pair of axially extending slots in its periphery in communication with said service port, said slots being blocked from communication with said inlet port by said first bore land and one of said slots being in communication with said exhaust port when said spool is in its closed position, the other of said slots being in communication with said inlet port and one slot being blocked from communication with said exhaust port by said second bore land when said spool is in its open position.

11. The valve of claim 10 wherein said one slot is enlarge'd at its axial end nearest said inlet port and said haust port.

12. The valve of claim 11 and further comprising an annular recess formed in said spool between said axial ends of said slots and wherein said slots open into said recess, said recess being in direct communication with said service port in all positions of said spool and said recess having communication with said inlet and outlet ports in the open and closed positions of said spool, respectively, by way of said one and other slots, respectively. 

1. A control valve of the type having a body with a bore, an inlet port communicating with said bore, a service port communicating with said bore and spaced in one axial direction from said inlet port by a first bore land and an exhaust port communicating with said bore and spaced in said one axial direction from said service port by a second bore land, characterized by: a spool reciprocatively mounted in said bore for axial movement between closed and open positions and having an axially extending slot in its periphery in communication with said service port, and first and second enlarged peripheral openings in said slot at its opposite axial ends, respectively, said first opening being blocked by said first bore land and said second opening being in full free flow communication with said exhaust port when said spool is in its closed position, said first opening being in full free flow communication with said inlet port and said second opening being blocked by said second bore land when said spool is in its open position.
 2. The valve of claim 1 and further characterized by an annular recess in said spool between and spaced axially from said openings.
 3. The valve of claim 2 wherein said recess communicates directly only with said service port and said recess is in fluid communication with said openings only through said slot.
 4. The valve of claim 1 wherein said openings are annular and extend transversely relative to the axis of said spool, the diameter of said openings being greater than the width of said slot.
 5. The valve of claim 4 wherein said openings extend transversely through said spool.
 6. The valve of claim 5 and further characterized by another slot on the diametrically opposite side of said spool from said first mentioned slot and extending axially between and in free flow communication with said openings.
 7. A control valve of the type having a body with a bore, an inlet port communicating with said bore, a service port communicating with said bore and spaced in one axial direction from said inlet port by a first bore land and an exhaust port communicating with said bore and spaced in said one axial direction from said service port by a second bore land, characterized by: a spool reciprocatively mounted in said bore for axial movement between closed and open positions and having, an axially extending slot in its periphery in communication with said service port, said slot being blocked from communication with said inlet port by said first bore land and said slot being in full fRee flow communication with said exhaust port when said spool is in its closed position, said slot being in full free flow communication with said inlet port and said slot being blocked from communication with said exhaust port by said second bore land when said spool is in its open position, said slot being in fluid communication with all said ports during a major part of the movement of said spool from said closed position to said open position.
 8. The valve of claim 7 and further characterized by an annular recess in said spool intermediate the axially opposite ends of said slot.
 9. The valve of claim 8 wherein said recess communicates directly only with said service port and said recess is in fluid communication with said inlet and exhaust ports only through said slot.
 10. A control valve of the type having a body with a bore, an inlet port communicating with said bore, a service port communicating with said bore and spaced in one axial direction from said inlet port by a first bore land and an exhaust port communicating with said bore and spaced in said one axial direction from said service port by a second bore land, characterized by: a spool reciprocatively mounted in said bore for axial movement between closed and open positions and having a pair of axially extending slots in its periphery in communication with said service port, said slots being blocked from communication with said inlet port by said first bore land and one of said slots being in communication with said exhaust port when said spool is in its closed position, the other of said slots being in communication with said inlet port and one slot being blocked from communication with said exhaust port by said second bore land when said spool is in its open position.
 11. The valve of claim 10 wherein said one slot is enlarged at its axial end nearest said inlet port and said other slot is enlarged at its axial end nearest said exhaust port.
 12. The valve of claim 11 and further comprising an annular recess formed in said spool between said axial ends of said slots and wherein said slots open into said recess, said recess being in direct communication with said service port in all positions of said spool and said recess having communication with said inlet and outlet ports in the open and closed positions of said spool, respectively, by way of said one and other slots, respectively. 